It is known to isolate a base from the supporting floor by placing air bags distributively around the perimeter of the base to isolate the base vibrations from the floor. A problem with such known air isolated bases is that leveling of the base, which is highly critical to the successful vibration test of the workpiece is only difficultly achieved, since each supporting bag must be adjusted in pressure to the right amount to have the base level overall, and overshooting or undershooting the precise pressure is commonplace, whereby all the bags must be readjusted. In addition, the deflation of the bags is a slow process and consumes an inordinate amount of time when the base is lowered or to be moved.